Sexual differentiation of prolactin responsiveness to thyrotropin releasing hormone (TRH) in the rat. Effects of postnatal testosterone on adenohypophyseal TRH receptor ontogenesis in male rats.

The influence of postnatal testosterone on thyrotropin releasing hormone (TRH)-induced prolactin (PRL) response was tested in male rats. Under urethane anesthesia following estradiol pretreatment, neonatally castrated males showed a female-like plasma PRL response 4-fold greater than in adult-castrated males. Substitution of testosterone reversed the NC effect. However, postnatal age-dependent difference was observed in the effect of testosterone. Testosterone produced a marked inhibition on PRL response when given at 2 or 4 weeks of life but not at earlier days. Determinations of adenohypophyseal PRL concentration and TRH receptor density revealed that testosterone inhibition occurred via its detrimental influence not on PRL concentration but on TRH receptor density. These results indicate that the sex-related difference in the rat PRL response to TRH ensues at least partially through inhibition by postnatal testosterone on the adenohypophyseal TRH receptor ontogenesis in male rats, and that there might be a functional dissociation in testosterone-dependent temporal development between two hypothalamic centers which independently regulate cyclic secretability and secretory reserve of PRL.